Method for operating a particulate filter disposed in an exhaust-gas region of an internal combustion engine and device for implementing the method

ABSTRACT

A method for operating a particulate filter disposed in an exhaust-gas region of an internal combustion engine and a device for implementing the method. Based on an oil signal provided by an oil sensor, an oil-consumption determination determines the oil consumption of the internal combustion engine. From the oil signal, an ash-load determination calculates a measure for the ash-load state of the particulate filter, which can be taken into account for the operation of the particulate filter, particularly in establishing a threshold value for the maximum permissible particulate-load state. Moreover, a filter replacement signal can be obtained from the ash-load state.

BACKGROUND INFORMATION

German Patent Application No. DE 199 06 287 describes a method and a device for controlling an internal combustion engine, in whose exhaust-gas region an exhaust-gas treatment device is arranged that includes a particulate filter which holds back the particulates contained in the exhaust gas. For proper operation of the particulate filter, it is necessary to know the particulate load state, which may be determined indirectly based on the differential pressure occurring at the particulate filter.

German Patent Application No. DE 102 48 431 describes a method for ascertaining the particulate-filter load state, in which the flow resistance of the exhaust gases is utilized as a measure for the particulate load state. The flow resistance is ascertained from the differential pressure occurring at the particulate filter and the exhaust-gas volumetric flow. Taking into consideration the exhaust-gas temperature, it is possible to obtain the exhaust-gas volumetric flow from the exhaust-gas mass flow rate which can be at least approximately calculated from at least one known operating characteristic of the internal combustion engine, e.g., from an air signal provided by an air sensor. The differential pressure occurring at the particulate filter is ascertained from a pressure signal provided by a pressure sensor situated upstream in front of the particulate filter, and the pressure downstream of the particulate filter which is determined with the aid of a pressure model of the exhaust-gas system existing downstream of the particulate filter, in which model the ambient-air pressure at the end of the exhaust-gas system is taken into account.

A particulate filter is regenerated by a burn-off of the particulates embedded in the particulate filter, which takes place in a temperature range of 500° C. -650° C., for example. German Patent Application No. DE 101 08 720 describes a method and a device for operating a particulate filter situated in an exhaust-gas region of an internal combustion engine, in which the starting point is at least one operating characteristic that indicates the state of the internal combustion engine and/or the state of the particulate filter, and from which a characteristic quantity is determined that describes the intensity of the particulate burn-off. The characteristic quantity is compared to a threshold value. If the threshold value is exceeded, measures are initiated for reducing the reaction speed in order to prevent overheating of the particulate filter, the measures being directed toward interventions to reduce the oxygen content in the exhaust gas.

German Patent Application No. DE 196 02 599 describes a method for determining a quantity of motor oil in an internal combustion engine, in which the oil level is measured by an oil sensor. The method makes it possible to ascertain the oil level comparatively accurately during operation of a motor vehicle.

An object of the present invention is to provide a method for operating a particulate filter disposed in an exhaust-gas region of an internal combustion engine and a device for implementing the method which permit the most precise possible ascertainment of the particulate load state of the particulate filter.

SUMMARY OF THE INVENTION

The procedure of the present invention provides that the oil level of the internal combustion engine is sensed by an oil sensor, that an oil-consumption determination unit determines the oil consumption of the internal combustion engine based on the oil signal provided by the oil sensor, and that an ash-load determination unit determines a measure for the ash-load state of the particulate filter from the oil consumption.

In addition to the particulates formed due to the combustion of the fuel in the cylinders of the internal combustion engine, ashes become embedded which result from the burning of motor oil, especially motor-oil additives. The ash accumulating in the particulate filter cannot be removed from the embedded particulates within the framework of regenerating the particulate filter. The knowledge of the ash load state may advantageously be taken into consideration during operation of the particulate filter.

One embodiment provides that a particulate-load determination unit determines the particulate-load state of the particulate filter, and that the ash-load state is taken into consideration when determining the particulate-load state. This measure is particularly advantageous if the particulate-load state is determined from the differential pressure occurring at the particulate filter. For example, the influence of the ash-load state on the differential pressure may be determined experimentally and utilized later for correction of the particulate-load state.

A further refinement of this embodiment provides that the exhaust-gas pressure upstream of the particulate filter is sensed by a pressure sensor, and that the exhaust-gas pressure downstream of the particulate filter is ascertained with the aid of a pressure model of the exhaust-gas system existing downstream of the particulate filter, in which model the ambient-air pressure occurring at the end of the exhaust-gas system is taken into account.

Another development provides that a measure for the temperature in the particulate filter is taken into account when ascertaining the particulate-load state. For example, the temperature may be calculated with the aid of an exhaust-gas temperature model. The temperature may moreover be sensed by at least one temperature sensor situated in the region of the particulate filter. The temperature sensor may be arranged in front of and/or in and/or after the particulate filter.

One particularly advantageous refinement provides that a threshold value predefined for the maximum permissible particulate-load state of the particulate filter or a predefined tolerance range is stipulated as a function of the ascertained ash-load state. This refinement takes into account that for safety reasons, the maximum permissible particulate-load state must be reduced as the ash-load state increases. Depending on the mechanical form of the particulate filter, with increasing ash-load state, the layer thickness of the embedded particulates increases given the same particulate-load state. During the necessary regeneration by burn-off of the particulates, with increasing thickness of the particulate layer, the danger of overheating may develop which can be decreased by reducing the maximum permissible particulate-load state.

Another further development of the procedure according to the present invention provides that, from the ascertained ash-load state, a particulate-filter service-life determination unit, using a filter-replacement signal, indicates a necessary replacement of the particulate filter.

The device according to the present invention for implementing the method according to the present invention relates first to a control device that is adapted for implementing the method.

In particular, the control device includes an oil sensor which provides an oil signal that is at least one measure for the oil level.

The device of the present invention further provides that a pressure sensor arranged upstream of the particulate filter is embodied as a differential-pressure sensor which ascertains the pressure difference between the exhaust-gas pressure upstream of the particulate filter and the ambient-air pressure.

The control device preferably includes at least one electrical memory in which the functions are stored as a computer program.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a technical environment in which a method of the present invention proceeds.

FIG. 2 shows a functional correlation between an ash-load state and a differential pressure.

FIG. 3 shows functional correlations between the particulate-load state and a differential pressure.

DETAILED DESCRIPTION

FIG. 1 shows an internal combustion engine 10 that has an air sensor 11 and a throttle valve 12 situated in its intake region. In the exhaust-gas region of internal combustion engine 10, a temperature sensor 21 and a pressure sensor 22 are provided upstream in front of a particulate filter 20.

A further exhaust-gas treatment device 23 is connected downstream of particulate filter 20.

A fuel-metering device 25 is assigned to internal combustion engine 10. Oil level 26 in internal combustion engine 10 is detected by an oil sensor 27.

A control device 30 receives an air signal ml from air sensor 11, a speed signal N from internal combustion engine 10, an oil signal H from the oil sensor, an exhaust-gas temperature T from the temperature sensor and a pressure signal p from pressure sensor 22. Control device 30 provides a throttle-valve signal DR to throttle valve 12, and a fuel signal mE to fuel-metering device 25.

Pressure sensor 22 provides pressure signal p as a function of exhaust-gas pressure pvPF of exhaust-gas mass flow msabg upstream of particulate filter 20 and as a function of ambient-air pressure pU. Downstream of particulate filter 20, exhaust-gas pressure pnPF of exhaust-gas mass flow msabg occurs after particulate filter 20. Ambient-air pressure pU occurs at the end of the exhaust-gas region.

Control device 30 includes an oil-consumption determination unit 31 that emits an oil-consumption signal 32 to an ash-load determination unit 33. Ash-load determination 33 provides an ash-load state mAsh to a particulate-load determination unit 34, a threshold establishment unit 35 and a particulate-filter service-life determination unit 41. The particulate-filter service-life determination provides a filter-replacement signal 42.

Particulate-load determination 34 determines particulate-load state mParticulate as a function of a differential pressure dp and as a function of exhaust-gas temperature T. Differential pressure dp is provided by a differential-pressure determination unit 36 as a function of pressure signal p and ambient-air pressure pU which is detected by an ambient-air-pressure sensor 37. Particulate-load state mParticulate and a threshold value Lim are fed to a regeneration coordinator 38 that emits a regeneration signal 39 to a regeneration control 40.

FIG. 2 shows a functional correlation between ash-load state mAsh and differential pressure dp which holds true given a constant exhaust-gas volumetric flow Vs.

FIG. 3 shows functional correlations between particulate-load state mParticulate and differential pressure dp. Ash-load state mAsh is indicated in unit percentage. A first characteristic curve 50 holds true for an ash-load state mAsh of zero %, a second characteristic curve 51 for an ash-load state mAsh of 20%, and a third characteristic curve 52 for an ash-load state mAsh of 50%. Threshold value Lim is plotted.

The method of the present invention operates as follows:

Control device 30 initially establishes fuel signal mE, fed to fuel-metering device 25, as well as throttle-valve signal DR as a function of air signal ml and/or speed signal N and/or torque setpoint signal MFa. During normal operation of internal combustion engine 10, exhaust-gas mass flow msabg carries along particulates that are formed during the combustion process of the fuel in internal combustion engine 10, especially upon combustion of fuel additives. The particulates become embedded in particulate filter 20.

Further exhaust-gas treatment device 23 situated downstream of particulate filter 20 is a catalytic converter or a muffler, for example.

The motor oil necessary for operating internal combustion engine 10 is monitored by oil sensor 27, at least with respect to fluid level 26. Oil sensor 27 emits oil signal H to control device 30, in which oil-consumption determination 31 determines oil-consumption signal 32.

The oil consumption is determined based on the decrease of fluid level 26. An increase of fluid level 26 due to a replenishment of consumed motor oil must be taken into account when evaluating a change in fluid level 26.

Ash-load determination 33 assigns ash-load state mAsh of particulate filter 20 to oil-consumption signal 32 with the aid of a correlation stored in ash-load determination 33. The correlation, not shown in more detail, is preferably determined experimentally.

The knowledge of ash-load state mAsh may be taken into consideration particularly advantageously during operation of particulate filter 20.

The increasing ash-load state impairs the storage capability and the working manner of particulate filter 20. Since it is not readily possible to remove the ash when particulate filter 20 is in the installed state, according to one refinement, ash-load state mAsh may be used to signal that it is necessary to replace particulate filter 20. After reaching a predefined ash-load state mAsh, particulate-filter service-life determination 41 outputs filter replacement signal 42.

Ash-load state mAsh may moreover be taken into account especially advantageously in the determination of particulate-load state mParticulate of particulate filter 20. In the exemplary embodiment, particulate-load determination 34 determines particulate-load state mParticulate as a function of differential pressure dp which occurs at particulate filter 20, and as a function of exhaust-gas temperature T. Ash-load state mAsh has an influence on differential pressure dp, which is shown in FIG. 2. The correlation is a function of the form of particulate filter 20. With the aid of experimentally verified calculations it was found that the case can occur that, starting from a low ash-load state mAsh, with increasing ash-load state mAsh, contrary to expectation, differential pressure dp initially assumes smaller values, and only with further increasing ash-load state mAsh does it rise to the anticipated higher values. One measure for particulate-load state mParticulate of particulate filter 20 is the flow resistance of particulate filter 20 which, according to the related art indicated at the outset, results from the quotient of differential pressure dp and exhaust-gas volumetric flow Vs.

Exhaust-gas volumetric flow Vs is calculated from exhaust-gas mass flow msabg, taking into account exhaust-gas temperature T that is detected by temperature sensor 21. In simple approximation, exhaust-gas mass flow msabg is proportional to air signal ml. To increase the accuracy, the fuel burned in internal combustion engine 10 may be taken into account with inclusion of fuel signal mE. If an exhaust-gas recirculation is present, the influence on exhaust-gas mass flow msabg may likewise be included.

The three characteristic curves 50, 51, 52 shown in FIG. 3 indicate the correlation between differential pressure dp and particulate-load state mParticulate in percentage. The correlation, shown in FIG. 2, between ash-load state mAsh and differential pressure dp is expressed in FIG. 3 in that, given low particulate-load state mParticulate, second characteristic curve 51, which corresponds to an ash-load state mAsh of 20%, is at a lower differential pressure dp than in the case of a lower ash-load state mAsh, which is plotted in FIG. 3 with first characteristic curve 50, corresponding to an ash-load state of zero %. According to FIG. 2, differential pressure dp first increases again with rising ash-load state mAsh. Therefore, third characteristic curve 52—as expected—lies above first characteristic curve 50, that is to say, the increased ash-load state, indicated with 50% in the example, given the same particulate-load state mParticulate, leads—as expected—to a higher differential pressure dp.

Predefined threshold value Lim is entered in FIG. 3. If, according to first characteristic curve 50, no ash is yet embedded in particulate filter 20, threshold value Lim may be set to the maximum permissible particulate-load state mparticulate of 100%. With increasing ash-load state mAsh, threshold value Lim for permissible particulate-load state mParticulate is reduced. In the exemplary embodiment shown according to FIG. 3, given an ash-load state mAsh of 50% according to third characteristic curve 52, threshold value Lim is reduced to, for example, 50% permissible particulate-load state mParticulate, as well. The correlation between the reduction of permissible particulate-load state mParticulate as a function of existing ash-load state mAsh may be ascertained theoretically or with the aid of experiments. The goal is to ensure a burn-off of the particulates during the regeneration, without the danger of overheating particulate filter 20. The reduction of permissible particulate-load state mParticulate in relation to existing ash-load state mAsh may deviate considerably from the pattern shown in FIG. 3. For example, given an ash-load state of 50% according to third characteristic curve 52, threshold value Lim could be at only 20% of maximum possible particulate-load state mParticulate.

Threshold value Lim set in threshold establishment 35 as a function of ash-load state mAsh, as well as particulate-load state mParticulate determined in particulate-load determination 34 are fed to regeneration coordinator 38 which ascertains whether a regeneration of particulate filter 20 is necessary. If this is the case, regeneration coordinator 38 emits regeneration signal 39 to regeneration control 40, which takes suitable measures for regenerating particulate filter 20.

For example, regeneration control 40 influences fuel signal mE which is supplied to fuel-metering device 25. For instance, fuel signal mE causes fuel-metering device 25 to release at least one secondary injection that is supposed to occur after a main injection. The post-injected fuel quantity burns—if at all—only in part in the cylinders of internal combustion engine 10. In each case, unburned fuel arrives in an optionally provided oxidation catalytic converter (not shown more precisely) situated upstream in front of particulate filter 20. The unburned fuel is converted in an exothermic reaction in the oxidation catalytic converter and contributes to the rise in the exhaust-gas temperature. Particulate filter 20 may itself have a catalytically acting coating on which the exothermic reaction takes place, so that direct heating of particulate filter 20 is possible.

Moreover, as a function of air signal ml, regeneration control 40 may influence throttle-valve signal DR for throttle valve 12 in such a way that the air flow is throttled, which leads to a further elevation of exhaust-gas temperature T. The ignition temperature of the particulates embedded in particulate filter 20 is reached by the elevation of the exhaust-gas temperature to 500-650° C., for example. The burn-off speed may be influenced by controlled influencing of the oxygen content in the exhaust gas. Regeneration control 40 adjusts the oxygen content by influencing throttle-valve signal DR.

Differential-pressure determination 36 calculates differential pressure dp, occurring at particulate filter 20, from pressure signal p provided by pressure sensor 22, from ambient-air pressure pU measured by ambient-air-pressure sensor 37, and with reference to a pressure model of the exhaust-gas system downstream of particulate filter 20. The exhaust-gas system downstream of particulate filter 20 includes further exhaust-gas treatment device 23 which is embodied at least as a catalytic converter and/or at least as a muffler, for instance. In forming the model, for example, the flow resistance of further exhaust-gas treatment device 23 and the flow resistance of the exhaust pipes are calculated as a function of exhaust-gas volumetric flow Vs, which—as already described—may be determined from exhaust-gas mass flow msabg with inclusion of exhaust-gas temperature T. Exhaust-gas pressure pnPF downstream of particulate filter 20, which is the goal of the calculation with the aid of the pressure model, may be determined from the flow resistance, exhaust-gas volumetric flow Vs, as well as known ambient-air pressure pU.

Ambient-air-pressure sensor 37 is disposed within control device 30, for example, since the ambient-air pressure may be utilized in particular for influencing fuel signal mE. Pressure sensor 22 is preferably in the form of a differential-pressure sensor which measures exhaust-gas pressure pvPF upstream of particulate filter 20 in comparison to ambient-air pressure pU and provides the pressure difference as pressure signal p. 

1. A method for operating a particulate filter situated in an exhaust-gas region of an internal combustion engine, the method comprising: using an oil sensor to detect an oil level of the internal combustion engine; using an oil-consumption determination unit to determine an oil-consumption signal as a measure for an oil consumption of the internal combustion engine, based on an oil signal provided by the oil sensor; and using an ash-load determination unit to determine a measure for an ash-load state of the particulate filter, based on the oil-consumption signal.
 2. The method according to claim 1, further comprising using a particulate-load determination unit to determine a particulate-load state of the particulate filter, the ash-load state being taken into consideration when determining the particulate-load state.
 3. The method according to claim 2, wherein the particulate-load state is determined from a pressure difference occurring at the particulate filter.
 4. The method according to claim 3, further comprising: detecting an exhaust-gas pressure upstream of the particulate filter by a pressure sensor; and determining an exhaust-gas pressure downstream of the particulate filter with reference to a model that takes into account an ambient-air pressure.
 5. The method according to claim 2, wherein a measure for a temperature in the particulate filter is taken into consideration when determining the particulate-load state.
 6. The method according to claim 1, further comprising establishing a threshold value predefined for a maximum permissible particulate-load state of the particulate filter as a function of the determined ash-load state.
 7. The method according to claim 1, further comprising using a particulate-filter service-life determination unit to determine and indicate a filter replacement signal, based on the ash-load state.
 8. A device for operating an internal combustion engine, comprising: an oil sensor to detect an oil level of the internal combustion engine; and at least one control device including an oil-consumption determination unit and an ash-load determination unit, the oil-consumption determination unit to determine an oil-consumption signal as a measure for an oil consumption of the internal combustion engine, based on an oil signal provided by the oil sensor, the ash-load determination unit to determine a measure for an ash-load state of a particulate filter, based on the oil-consumption signal.
 9. The device according to claim 8, wherein the oil signal is at least one measure for the oil level of the internal combustion engine.
 10. The device according to claim 8, further comprising a differential-pressure sensor situated upstream of the particulate filter for determining a pressure difference between an exhaust-gas pressure upstream of the particulate filter and an ambient-air pressure. 